linux-kernel - Re: [PATCH 1/3] introduce for_each_process_thread

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Message-ID: <20160802115850.GI6862@twins.programming.kicks-ass.net>
Date:	Tue, 2 Aug 2016 13:58:50 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Anderson <anderson@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Wang Shu <shuwang@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] introduce for_each_process_thread_{break,continue}()
 helpers

On Mon, Jul 25, 2016 at 06:23:48PM +0200, Oleg Nesterov wrote:
> +void for_each_process_thread_continue(struct task_struct **p_leader,
> +				      struct task_struct **p_thread)
> +{
> +	struct task_struct *leader = *p_leader, *thread = *p_thread;
> +	struct task_struct *prev, *next;
> +	u64 start_time;
> +
> +	if (pid_alive(thread)) {
> +		/* mt exec could change the leader */
> +		*p_leader = thread->group_leader;
> +	} else if (pid_alive(leader)) {
> +		start_time = thread->start_time;
> +		prev = leader;
> +
> +		for_each_thread(leader, next) {
> +			if (next->start_time > start_time)
> +				break;
> +			prev = next;
> +		}

This,

> +		*p_thread = prev;
> +	} else {
> +		start_time = leader->start_time;
> +		prev = &init_task;
> +
> +		for_each_process(next) {
> +			if (next->start_time > start_time)
> +				break;
> +			prev = next;
> +		}

and this, could be 'SPEND_TOO_MUCH_TIME' all by themselves.

Unlikely though, nor do I really have a better suggestion :/

> +
> +		*p_leader = prev;
> +		/* a new thread can come after that, but this is fine */
> +		*p_thread = list_last_entry(&prev->signal->thread_head,
> +						struct task_struct,
> +						thread_node);
> +	}
> +
> +	put_task_struct(leader);
> +	put_task_struct(thread);
> +}